Latest update- I have a Beretta 92SF with a couple of extra magazines. I took one of the 18 round mags and drilled a hole to match the Zastava's. I did not get it completely flat across the top, but did get what appears to be the correct height, with a wide enough cut.
The mags are quite tough, took a carbide drill in the drill press.
After drilling the hole, had to draw a file through a few times to smooth out the burrs in the inside of the magazine.
It locks up with just the slightest gap at the base (nothing I haven't seen with a S&W), feeds snapcaps from the magazine, and holds the slide back. So far, so good. I will find my dremel to better square off the top of the notch.
And yes, it can still run in the Beretta.
As an aside, I've heard it stated that the Beretta magazines can also fit in the 3rd Gen S&W's, and it does seem the case. Again, would need to slice another notch for the magazine catch to make it work.
Going the opposite direction, the S&W factory mags seem the slightest bit tight in the Beretta and Zastava; I have to pull them out instead of dropping free.
So next project: find some of these infamous sub-$10 M9 mags that people talk about, and see if I can make some universal (sort of) range mags for a few of my pistols.
If only the CZ 75 would take these... but I have plenty of mags for that.
pics to come